New iron(II) cyclopentadienyl derivative complexes: Synthesis and antitumor activity against human leukemia cancer cells

Iron(II)-cyclopentadienyl compounds are cytotoxic against colon adenocarcinoma cell lines: Ethylenebis(diphenylphosphane) vs. triphenylphosphane

Structure-activity studies aiming to understand the role of each coligand in the formulation of new metallodrugs is an important subject. In that frame, six new compounds with general formula [Fe(η5-C5H5)(dppe)(L)][CF3SO3] with L = benzonitriles (1-4) or carbon monoxide (5) and compound [Fe(η5-C5H5)(CO)(PPh3)2][CF3SO3] (6) were synthesized and compared with three other previously reported compounds [Fe(η5-C5H5)(CO)(L)(PPh3)][CF3SO3]. We were particularly interested in assessing the effect of dppe vs. (PPh3 + CO) for this set of compounds. For that, all compounds were tested against two human colon adenocarcinoma cell lines, Colo205 and the refractile Colo320 (expressing ABCB1, an efflux pump causing multidrug resistance), showing IC50 values in the micromolar range. The presence of dppe in the compound's coordination sphere over (PPh3 + CO) allows for more redox stable compounds showing higher cytotoxicity and selectivity, with improved cytotoxicity towards resistant cells that is not related to the inhibition of ABCB1. Further studies with GSH and H2O2 for selected compounds indicated that their antioxidant ability is not probably the main responsible for their cytotoxicity.

First iron(II) organometallic compound acting as ABCB1 inhibitor

Five new iron (II) complexes bearing imidazole-based (Imi-R) ligands with the general formula [Fe(η⁵-C₅H₅)(CO)(PPh₃)(Imi-R)][CF₃SO₃] were synthesized and fully characterized by several spectroscopic and analytical techniques. All compounds crystallize in centrosymmetric space groups in a typical "piano stool" distribution. Given the growing importance of finding alternatives to overcome different forms of multidrug resistance, all compounds were tested against cancer cell lines with different ABCB1 efflux pump expression, namely, the doxorubicin-sensitive (Colo205) and doxorubicin-resistant (Colo320) human colon adenocarcinoma cell lines. Compound 3 bearing 1-benzylimidazole was the most active in both cell lines with IC₅₀ values of 1.26 ± 0.11 and 2.21 ± 0.26 μM, respectively, being also slightly selective against the cancer cells (vs. MRC5 normal human embryonic fibroblast cell lines). This compound, together with compound 2 bearing 1H-1,3-benzodiazole, were found to display very potent ABCB1 inhibitory effect. Compound 3 also showed the ability to induce cell apoptosis. Iron cellular accumulation studies by ICP-MS and ICP-OES methods revealed that the compounds' cytotoxicity is not related to the extent of iron accumulation. Yet, it is worth mentioning that, from the compounds tested, 3 was the only one where iron accumulation was greater in the resistant cell line than in the sensitive one, validating the possible role of ABCB1 inhibition in its mechanism of action.

Coordination compounds of biogenic metals as cytotoxic agents in cancer therapy

The review summarizes the data on the structures and methods for the synthesis of compounds with anticancer activity based on biogenic metals, which can replace platinum drugs prevailing in cytotoxic therapy. The main focus is given to the comparison of the mechanisms of the cytotoxic action of these complexes, their efficacy and prospects of their use in clinical practice. This is the first systematic review of cytotoxic zinc, iron, cobalt and copper compounds. The structure – activity relationships and the mechanisms of antitumour action are formulated for each type of metal complexes.

The bibliography includes 181 references.

Easily Available, Amphiphilic Diiron Cyclopentadienyl Complexes Exhibit in Vitro Anticancer Activity in 2D and 3D Human Cancer Cells through Redox Modulation Triggered by CO Release

A straightforward two-step procedure via single CO removal allows the conversion of commercial [Fe2 Cp2 (CO)4 ] into a range of amphiphilic and robust ionic complexes based on a hybrid aminocarbyne/iminium ligand, [Fe2 Cp2 (CO)3 {CN(R)(R')}]X (R, R'=alkyl or aryl; X=CF3 SO3 or BF4 ), on up to multigram scales. Their physicochemical properties can be modulated by an appropriate choice of N-substituents and counteranion. Tested against a panel of human cancer cell lines, the complexes were shown to possess promising antiproliferative activity and to circumvent multidrug resistance. Interestingly, most derivatives also retained a significant cytotoxic activity against human cancer 3D cell cultures. Among them, the complex with R=4-C6 H4 OMe and R'=Me emerged as the best performer of the series, being on average about six times more active against cancer cells than a noncancerous cell line, and displayed IC50 values comparable to those of cisplatin in 3D cell cultures. Mechanistic studies revealed the ability of the complexes to release carbon monoxide and to act as oxidative stress inducers in cancer cells.

A New Family of Iron(II)-Cyclopentadienyl Compounds Shows Strong Activity Against Colorectal and Triple Negative Breast Cancer Cells

A family of compounds with the general formula [Fe(η5-C5H5)(CO)(PPh3)(NCR)]+ has been synthesized (NCR = benzonitrile (1); 4-hydroxybenzonitrile (2); 4-hydroxymethylbenzonitrile (3); 4-aminobenzonitrile (4); 4-bromobenzonitrile (5); and, 4-chlorocinnamonitrile (6)). All of the compounds were obtained in good yields and were completely characterized by standard spectroscopic and analytical techniques. Compounds 1, 4, and 5 crystallize in the monoclinc P21/c space group and packing is determined by short contacts between the phosphane phenyl rings and cyclopentadienyl (compounds 1 and 4) or π-π lateral interactions between the benzonitrile molecules (complex 5). DFT and TD-DFT calculations were performed to help in the interpretation of the experimental UV-Vis. data and assign the electronic transitions. Cytotoxicity studies in MDA-MB-231 breast and SW480 colorectal cancer-derived cell lines showed IC50 values at a low micromolar range for all of the compounds in both cell lines. The determination of the selectivity index for colorectal cells (SW480 vs. NCM460, a normal colon-derived cell line) indicates that the compounds have some inherent selectivity. Further studies on the SW480 cell line demonstrated that the compounds induce cell death by apoptosis, inhibit proliferation by inhibiting the formation of colonies, and affect the actin-cytoskeleton of the cells. These results are not observed for the hydroxylated compounds 2 and 3, where an alternative mode of action might be present. Overall, the results indicate that the substituent at the nitrile-based ligand is associated to the biological activity of the compounds.

Anticancer Potential of Diiron Vinyliminium Complexes

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram-scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC₅₀ values in the low-to-mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non-tumoral human embryonic kidney (HEK-293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron-based anticancer candidates.

Influence of the substituent on the phosphine ligand in novel rhenium(i) aldehydes. Synthesis, computational studies and first insights into the antiproliferative activity

Cyrhetrenyl phosphine derivatives were synthesized and evaluated as potential anticancer agents. Electrochemical and computational studies were carried out.

pH-Switchability and Second-Order Nonlinear Optical Properties of Monocyclopentadienylruthenium(II)/iron(II) Tetrazoles/Tetrazolates: Synthesis, Characterization, and Time-Dependent Density Functional Theory Calculations

Tetrazole/tetrazolate monocyclopentadienyliron(II) and ruthenium(II) compounds of general formulas [(η⁵-C₅H₅)M(dppe)(N₄(H)CC₆H₄NO₂)][PF₆]/[(η⁵-C₅H₅)M(dppe)(N₄CC₆H₄NO₂)] were investigated for their pH-switching second-order nonlinear optical (SONLO) properties. Compounds [(η⁵-C₅H₅)M(dppe)(N₄CC₆H₄NO₂)] (M = Fe, Ru) and compound [(η⁵-C₅H₅)Ru(dppe)(N₄(H)CC₆H₄NO₂)][PF₆] were fully characterized by (¹H-, ¹³C-, ³¹P-) NMR, cyclic voltammetry, and elemental analysis, and compounds [(η⁵-C₅H₅)Fe(dppe)(N₄CC₆H₄NO₂)] and [(η⁵-C₅H₅)Ru(dppe)(N₄(H)CC₆H₄NO₂)][PF₆] were further characterized by single-crystal X-ray diffraction; the synthesis of [(η⁵-C₅H₅)Fe(dppe)(N₄(H)CC₆H₄NO₂)][PF₆] was unsuccessful. Time-dependent density functional theory calculations were performed using PBE0 and CAM-B3LYP functionals to evaluate the first hyperpolarizability (β_tot) of the tetrazole/tetrazolate complexes and for a detailed analysis of the experimental data. Both functionals predict (i) high first hyperpolarizabilities for the tetrazolate complexes [(η⁵-C₅H₅)M(dppe)(N₄CC₆H₄NO₂)], with β_tot[Ru] ≈ 1.2β_tot[Fe], and (ii) a 3-fold reduction in β_tot[Ru] upon protonation, in complex [(η⁵-C₅H₅)Ru(dppe)(N₄(H)CC₆H₄NO₂)]⁺, forecasting [(η⁵-C₅H₅)Ru(dppe)(N₄CC₆H₄NO₂)]/[(η⁵-C₅H₅)Ru(dppe)(N₄(H)CC₆H₄NO₂)]⁺ complexes as on/off, pH-switchable SONLO forms.

Tracking antitumor metallodrugs: promising agents with the Ru(II)- and Fe(II)-cyclopentadienyl scaffolds

Research on the field of metal complexes for the treatment of cancer diseases has attracted increasing interest due to the urgency in finding more efficient and selective treatments. Owing to their wide structural diversity, organometallic complexes appear as potential alternatives to the design of new anticancer candidates. Herein, we review recent progress in our work toward the development of new drugs based on Ru(II)- and Fe(II)-cyclopentadienyl scaffolds. Their design and chemical properties are reviewed and correlated with their biological effects, in particular the key role that coligands play in the overall behavior of the complex.

Preparation of diazoalkane complexes of iron(ii)

The preparation of diazoalkane complexes of iron(ii) and their reactivity toward acrylonitrile are described.

Cyclopentadienyl-ruthenium(II) and iron(II) organometallic compounds with carbohydrate derivative ligands as good colorectal anticancer agents

New ruthenium(II) and iron(II) organometallic compounds of general formula [(η(5)-C5H5)M(PP)Lc][PF6], bearing carbohydrate derivative ligands (Lc), were prepared and fully characterized and the crystal structures of five of those compounds were determined by X-ray diffraction studies. Cell viability of colon cancer HCT116 cell line was determined for a total of 23 organometallic compounds and SAR's data analysis within this library showed an interesting dependency of the cytotoxic activity on the carbohydrate moiety, linker, phosphane coligands, and metal center. More importantly, two compounds, 14Ru and 18Ru, matched oxaliplatin IC50 (0.45 μM), the standard metallodrug used in CC chemotherapeutics, and our leading compound 14Ru was shown to be significantly more cytotoxic than oxaliplatin to HCT116 cells, triggering higher levels of caspase-3 and -7 activity and apoptosis in a dose-dependent manner.